On-Tissue Derivatization via Electrospray Deposition for Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry Imaging of Endogenous Fatty Acids in Rat Brain Tissues

Abstract

Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry imaging (MSI) is used for the multiplex detection and characterization of diverse analytes over a wide mass range directly from tissues. However, analyte coverage with MALDI MSI is typically limited to the more abundant compounds, which have m/z values that are distinct from MALDI matrix-related ions. On-tissue analyte derivatization addresses these issues by selectively tagging functional groups specific to a class of analytes, while simultaneously changing their molecular masses and improving their desorption and ionization efficiency. We evaluated electrospray deposition of liquid-phase derivatization agents as a means of on-tissue analyte derivatization using 2-picolylamine; we were able to detect a range of endogenous fatty acids with MALDI MSI. When compared with airbrush application, electrospray led to a 3-fold improvement in detection limits and decreased analyte delocalization. Six fatty acids were detected and visualized from rat cerebrum tissue using a MALDI MSI instrument operating in positive mode. MALDI MSI of the hippocampal area allowed targeted fatty acid analysis of the dentate gyrus granule cell layer and the CA1 pyramidal layer with a 20-μm pixel width, without degrading the localization of other lipids during liquid-phase analyte derivatization.

Improving the analyte ion signal in matrix‐assisted laser desorption/ionization imaging mass spectrometry via electrospray deposition by enhancing incorporation of the analyte in the matrix

“…These spectra did not show signal from the analytes, indicating the analytes did not move laterally, at least over the approximately 50 μm distance investigated. This is supported by experiments using ESD to apply derivatizion reagents prior to matrix application by other methods, in which no movement of the analyte was seen at a lateral resolution of 20 microns …”

“…This is supported by experiments using ESD to apply derivatizion reagents prior to matrix application by other methods, in which no movement of the analyte was seen at a lateral resolution of 20 microns. [38] Despite the potential of attaining incorporation with only the matrix spray by ESD, decoupling the application of the matrix and the application of the solvent to a sample allows for the independent optimization of each step. Essentially, the most homogeneous matrix layer can be created over the sample initially with no concern for promoting incorporation of the analyte and the matrix.…”

Mass Spectrometry Imaging: A Review of Emerging Advancements and Future Insights

“…29 N-glycans (Figure 2), fatty acids, and neurotransmitters have all been targets through other, unique on-tissue assays. 28,42,52 Compared to the traditional spraying of reagent, which usually produces poor spatial resolutions (>100 µ m), electrospray deposition has been successfully utilized to derivatize fatty acids while achieving a high spatial resolution (20 µ m). 42 …”

“…216 Lipids also have the potential to show tumor boundaries, specifically in breast cancer. 217 Because of their diverse structure, several common ionization sources, including MALDI, 1,20,42,97 DESI, 22,217,218 SIMS, 219–221 and IR-MALDESI, 18,19 have found success in lipid imaging. Notably, newly developed laser spray ionization (LSI), with its simple sample preparation, is becoming more commonly used for lipids as well.…”

Recent advances in high-throughput mass spectrometry that accelerates enzyme engineering for biofuel research

“…The underlying technical difficulties are due to the low molecular weight, low ionization efficiency, and high volatility of these molecules. To overcome these difficulties, assays need be developed to enhance MALDI MS detection, including chemical derivatization [69], the use of nonclassical MALDI matrices such as nanoparticles [70], and detection of easy-to-ionize metabolic precursors such as membrane lipid species [71]. Alternatively, ESI MS assays may also be developed to screen fatty-acid derived products.…”